The present invention relates to an individual coil type ignition coil for use in an engine which is prepared for every ignition coil each of an engine and is used by directly connecting to said respective ignition coil and an engine having a plastic head cover which is related technically to those ignition coils.
Recently, an individual ignition coil type ignition coil for use in an engine has developed such an ignition coil is individually and directly connected to each of the ignition coils which are introduced to plug holes of the engine. In this kind of the ignition coil, a distributor becomes unnecessary, as a result at the distributor and a high tension cord for the distributor etc. a supply energy for the ignition coil does not fall down. In addition to these, without a consideration about a fall down of the ignition energy, it can design the ignition coil. Accordingly, a coil capacity can be made small and a small scale structure of the ignition coil can be devised, and further by an abolishment of the distributor, a rationalization of a component mounting space in an interior portion of an engine room can be devised.
In the above stated individual ignition type ignition coil, so as to mount the ignition coil by introducing at least a part of the ignition coil against to a plug hole, it is called as a plug hole coil. Further, so as to insert a coil portion to the plug hole, the ignition coil is called as a pencil type ignition coil which is long and thin in a pencil shape. This pencil type ignition coil has a center core (a magnetic core in which plurality of silicon steel sheets are laminated), a primary coil and a secondary coil at an interior portion of a long and narrow cylindrical shape coil case. The primary coil and the secondary coil are wounded to a respective bobbin and are arranged concentrically at a periphery of the center core. In the coil case for receiving the primary coil and the secondary coil, by potting and hardening an insulation resin and by filling up an insulation oil, thereby an insulation performance of the ignition coil is guaranteed. As the prior arts, for example, there are Japanese patent laid-open publication No. Hei 8-255719, Japanese patent laid-open publication No. Hei 9-7860, Japanese patent laid-open publication No. Hei 8-97,057, Japanese patent laid-open publication No. Hei 8-144910 and Japanese patent laid-open publication No. Hei 8-203757. Further, in the pencil type ignition coil, there is taken into a consideration in which to restraint the leakage fluxes passing an outer periphery of the coil a side core is provided at the outer periphery of the coil case.
In the pencil type ignition coil,there is two types, one of them in which the primary coil is arranged at an inner side and the secondary coil is arranged at an outer side, and another of them in which the secondary coil is arranged at an inner side and the primary coil is arranged at an outer side. A latter type (a structure of secondary wire is arranged inside primary wire) has an advantage merit about an output characteristic in comparison with a former type (a structure of secondary wire is arranged outside primary wire).
Namely, in case of the pencil type ignition coil in which an insulation resin (for example, an epoxy resin) is potted and hardened to a coil constitution member, as shown in FIG. 7, in the structure in which the secondary wire is arranged outside the primary wire, the primary coil, the epoxy resin, a secondary bobbin, the secondary coil, the epoxy resin, a coil case, and a side core are provided from the inner side in order. In this structure, an electrostatic floating capacitance generates between the secondary coil and the primary coil which is arranged at an inner side of the secondary coil and has a low voltage (this is regarded as a substantial ground voltage), and further an electrostatic floating capacitance generates between the secondary coil and the side core (a ground voltage). As a result, in comparison with the structure in which the secondary wire is arranged inside the primary wire, the electrostatic floating capacitance of the side core follows superfluous, accordingly the electrostatic floating capacitance of the structure in which the secondary wire is arranged outside the primary wire tends to become large. (On the other hand, in the structure in which the secondary wire is arranged inside the primary wire, an electrostatic floating capacitance generates between the secondary coil and the primary coil, and between the primary coil and the side core both the primary coil and the side core has the ground voltages, the electrostatic floating capacitance does not generate substantially).
A secondary voltage output and a secondary voltage rising speed are affected by the electrostatic floating capacitance and the more the electrostatic floating capacity becomes large, the more the output lowers and a delay in the rising generates. As a result, the structure having the small electrostatic floating capacitance in which the secondary wire is arranged inside the primary wire is considered to suit for a small scale structure and a high output performance.
In the case of the structure in which the secondary wire is arranged inside the primary wire, in the structure between the secondary bobbin and the center core, it is an important problem that how an anti-heat shock performance and a mitigation of electric field concentration are compatible with.
The above stated secondary bobbin has a role of an insulation of a high voltage generated in the secondary coil from the center core. In a case where a gap is provided between the secondary bobbin and the center core, a difference in an electric field strength (an electric field strength of a gap portion becomes extremely large, an electric field concentration) generates, a dielectric break down generates at the gap portion between the secondary coil and the center core. To prevent the dielectric break down, it is necessary to fill up an insulation member between the secondary bobbin and the center core and to mitigate the electric field concentration.
However, in the case where the resin is filled up between the secondary bobbin and the center core, according to a difference between the coefficient of linear thermal expansion (13xc3x9710xe2x88x926 mm/xc2x0 C.) of the center core and the coefficient of linear thermal expansion of the resin, there is an axioms that cracks cause in the resin and the dielectric break down generates. As such a crack prevention countermeasure, it is conceivable that by blending a silica filler etc. the coefficient of linear thermal expansion of the resin approaches to that of the center core. However, in the above case, a flowability of a resin molding lowers and in particularly there is a problem that it is difficult to pot the resin to a gap (one figure level mm at a decimal point) between the center core and the secondary bobbin which is a minute clearance.
Then the inventors of the present invention have devised a method in which a flexible epoxy resin having a glass transition point at less than a normal temperature (20xc2x0 C.) and young""s modulus of 1xc3x97108 (Pa) at more than the normal temperature was filled up between the secondary bobbin and the center core. (For example, Japanese patent application No. Hei 7-326800, Japanese patent application No. Hei 8-249733). Herein, the flexible epoxy resin is defined as a soft epoxy resin which has a soft state at the normal temperature. Such a soft epoxy resin is injected, for example, under a vacuum condition to get extremely rid of voids (a vacuum potting type).
The soft epoxy resin has the superior anti-heat shock performance (the heat shock absorption, the heat shock mitigation) against to a repeated thermal stress since the soft epoxy resin has an elasticity. By an employment of the above stated soft epoxy resin, the heat shock against to the center core and the heat shock against to the secondary bobbin can be mitigated and further by an employment of the material having a superior adhesion performance, it can prevent the clearance occurrence between the center core and the secondary bobbin, but on the other hand since an insulation performance is low in comparison with a bobbin material, it is desirable to make thin to the utmost and a thickness of the second bobbin is assured and then the insulation performance between the secondary coil and the center core.
Objects of the Present Invention are that
(1) An object of the present invention is that, in an individual ignition type ignition coil (for example, a plug hole coil) in which the above stated secondary wire being arranged inside the primary wire structure is employed and is led into a plug hole, an anti-heat shock performance and a relaxation of electric field concentration (an insulation performance) between a secondary coil and a center coil can be improved and a quality (a reliability) and a working productivity in manufacturing can be heightened.
(2) Another object is that, even in an engine having a plastic cylinder head cover, an individual ignition type ignition coil can be adopted without any obstacle and a light weight structure of the engine can be realized.
A first invention (an invention relating to claim 1) is that in an individual ignition type ignition coil for use in an engine in which a center core, a secondary coil wound on a secondary bobbin and a primary coil wound on a primary bobbin are installed concentrically from an inner side of a coil case in order, and said ignition coil is connected directly to a respective spark plug of said engine, the ignition coil for use in the engine characterized in that, an insulation resin is filled up between said secondary bobbin and side center core, and a thickness of side secondary bobbin is changed with an inclined shape in such a manner in which an inner diameter of said secondary bobbin is formed larger at a potting side of said insulation resin and is formed small toward for an opposition side of said potting side.
It is necessary to thin to the utmost the insulation resin which is filled up between the secondary bobbin and the center core, for example the soft epoxy resin is used as stated in the above, to secure the secondary bobbin thickness (to secure the insulation performance). Such a secondary bobbin thickness is desirable to secure at the minimum of 0.1 mm to guarantee a linear thermal expansion difference absorption (the heat shock mitigation) against the center core and the secondary bobbin and the absorption in the size scattering in a mass production of a bobbin material and the core and a smoothness of the vacuum potting.
To satisfy the above stated requirements, the gap formed between the secondary bobbin and the center core becomes one having mm ({fraction (1/10)} mm order) of one figure of a decimal point and to this extremely narrow gap the insulation resin is potted and hardened. According to the present invention, to an inner diameter portion of the secondary bobbin, since an inclination having an inner diameter difference in which a potting side is formed large and it becomes smaller toward an opposing side, in the gap formed between the secondary bobbin and the center core, the insulation resin potting side is formed large and it becomes smaller gradually toward the opposing side, accordingly by widening a width of the resin potting and the smoothness of the resin potting can be improved. Further, even the width of the resin potting is widened, the gap between the center core and the secondary bobbin is narrowed gradually, the thin layer structure of the insulation resin can be held to the utmost.
A second invention (an invention relating to claim 2) is that in addition to the above stated first invention, in said secondary bobbin side, a secondary coil low voltage side is a potting side of said insulation resin, said secondary bobbin has an inclination with a difference in inner diameter of said secondary bobbin in such a manner in which an inner diameter of said secondary bobbin is formed large at said secondary coil voltage side and is formed small toward for a secondary coil high voltage side, and said secondary bobbin forms a bobbin structure in which a thickness of said secondary bobbin is formed thin at said secondary coil low voltage side and is formed thick toward for said secondary coil high voltage side.
With this construction, in addition to the operations (a compatibility of the flowability improvement of the insulation resin and the thin layer structure) according to the above stated first invention, next operations are carried out.
A coil portion (a portion comprised of a coil case, a coil accommodated in the coil case, and a core etc.) of the ignition coil is connected directly to a spark plug of a cylinder head and receives a thermal affect of an engine combustion. In a severe operation condition under an outside temperature of 40xc2x0 C., a second speed 55 km/h at an upslope of 10%, the outer surface temperature of the coil case is 140xc2x0 C. at a portion where the coil case is connected directly to the ignition coil nearest to the engine, the outer surface temperature is 130xc2x0 C. at a vicinity of a high voltage side of the secondary coil which is remote just a little from the spark plug, the outer surface temperature is 110xc2x0 C. at a low voltage side of the secondary coil which is provided at an outer side of the cylinder head and a distance from the secondary coil high voltage side is 80-105 mm degree, and the outer surface temperature is 100xc2x0 C. at an ignition circuit case which is provided on above the vicinity of the high voltage side.
As a result, in the secondary bobbin it can be expected fully that the secondary coil high voltage side presents a higher temperature condition compared with the secondary coil low voltage side and then the insulation performance lowers and further the thermal stress becomes large. However, according to the present invention, the secondary bobbin thickness at the secondary coil low voltage side is formed thin and the secondary bobbin thickness is formed thick toward the secondary coil high voltage side, with the thickness increase part the insulation performance and the anti-thermal stress at the secondary coil high voltage side is heightened and accordingly it can cope with the above stated thermal affect due to the engine combustion.
A third invention (an invention relating to claim 3) is that, in the secondary wire being arranged inside primary wire structure individual ignition type ignition coil for use in the engine similar to the first and the second inventions, as an insulation resin for potting between said secondary bobbin and center core, said insulation resin is an insulation resin having a glass transition point Tg which satisfy a condition of [an allowable stress of said secondary bobbin greater than a generation stress (from xe2x88x9240xc2x0 C. to a glass transition point of said insulation resin)]. The condition establishment reasons of the above stated Tg are as following.
As the above stated insulation resin (herein, the insulation resin is one which is filled up between the secondary bobbin and the center core), to form the thin layer structure and to mitigate to the heat shock (a thermal expansion, a contraction difference according to the temperature change in the engine room; a thermal stress) according to the coefficient of linear thermal expansion difference between the center core and the secondary bobbin, it can cope with to give an elasticity (a flexibility) by softening the resin.
To soften the above stated insulation resin, a glass transporting point Tg and Young""s modules after a molding (a thermal hardening) of the resin are important factors. In other words, Tg is a standard as a softening point of the material and more than Tg the resin is softened and the more Young""s modulus at the softened condition is small, the more the elasticity (the flexibility) can be carried out.
Accordingly, in a case of the above stated pencil type coil, since the coil is mounted on the engine room having a severe temperature environment (in general, it is xe2x88x9240xc2x0 C.-130xc2x0 C.), to obtain the anti-heat shock performance, it is desirable that the above stated insulation resin to have Tg at the low temperature and at the temperature range of the use environment of the engine to have the soft condition to the utmost. However, it is not unnecessary to lower Tg less than xe2x88x9240xc2x0 C. (in the other words, it is unnecessary to soften the insulation resin until less than xe2x88x9240xc2x0 C.). The reasons will be explained referring to FIG. 8.
FIG. 8(a) is a characteristic view showing behaviors of the insulation resin between the secondary bobbin, and the center core and the secondary bobbin by expecting the temperature of the engine room in which the secondary wire being arranged inside primary wire structure individual ignition type ignition coil to have xe2x88x9240xc2x0 C.-xe2x88x9230xc2x0 C., and this characteristic has studied clearly by the inventors of the present invention. FIG. 8(b) is an explanatory view for compensating the above stated behavior characteristic.
FIG. 8(b) shows a condition the secondary bobbin having the secondary wire being arranged inside primary wire structure is contracted to a center core side by accompanying with the lowering of the surrounding temperature, and when the insulation resin between the secondary bobbin and the center core presents the softening condition (more than the glass transition point Tg), since the contraction (the deformation toward the center core side) during the temperature drop is received by the above stated insulation resin, it can admit that the stress (the thermal stress) of the secondary bobbin is not generated substantially.
The engine stops and the temperature drop goes, for example in a cold district, the above stated insulation resin of the pencil type coil becomes less than Tg, the insulation resin transfers to the glass condition and to obstruct the contraction of the secondary bobbin, the stress (the thermal stress) generates on the secondary bobbin. This stress "sgr" is expressed as following in the relationship of Young""s modulus E and a strain xcex5.
"sgr"=Exc3x97xcex5=Exc3x97xcex1xc3x97T
xcex1 is the coefficient of linear thermal expansion of the secondary bobbin and T is the temperature change (the temperature difference).
For example, in the temperature change (xe2x88x9240xc2x0 C.-130xc2x0 C.) shown in FIG. 8(a), in a case where the glass transition point Tg of the insulation resin between the secondary bobbin and the center core is set at 130xc2x0 C., since the stress of the secondary bobbin generates at a range of 130xc2x0 C.-xe2x88x9240xc2x0 C., then the maximum stress "sgr"MAX appears. In a case where Tg is set to Tg1, (Tg1 less than 130xc2x0 C.) a stress "sgr"1 generates at a range (a temperature difference T1) of Tg1-xe2x88x9240xc2x0 C. (at a range of from 130xc2x0 C. to Tg1, since the contraction of the secondary bobbin is not obstructed, it appears substantially no stress). Similarly to in a case where Tg is set to Tg2, (Tg2 greater than Tg1) a stress "sgr"2 generates at a range (a temperature difference T2) of Tg2-xe2x88x9240xc2x0 C. (at a range of from 130xc2x0 C. to Tg2, since the contraction of the secondary bobbin is not obstructed, it appears substantially no stress).
For example, in a case where an allowance stress "sgr"0 is "sgr"1 less than "sgr"0 less than "sgr"2, when Tg of the insulation resin between the secondary bobbin and the center core is less than Tg1 (xe2x88x9240xc2x0 C. less than Tg less than Tg1), the generation stress "sgr" of the secondary bobbin is small than the allowable stress "sgr"0, the generation of the damage of the secondary bobbin can be obstructed. In this case, a range of from xe2x88x9240xc2x0 C. to Tg1, even the insulation resin between the secondary bobbin and the center core is hardened and the heat shock mitigation operation is out, since the temperature range is narrow, the heat shock weakens the soundness of the secondary bobbin and the center core can be held. Herein, in FIG. 8(a), the above stated Tg1 is a position of xe2x88x9225xc2x0 C., this is one example where the insulation resin is one specified material, however it is not limited to this example.
As stated in the above, the glass transition point which is a boundary point for softening the anti-heat shock performance of the insulation resin, in relationship to the stress generated on the secondary bobbin, is Tg which satisfies a condition [the allowable stress "sgr"0 of the secondary bobbin greater than the generation stress "sgr" of the secondary bobbin at (from xe2x88x9240xc2x0 C. to the glass transition point of the insulation resin)], the compatibility between the anti-heat shock performance and the soundness of the secondary bobbin against to the secondary bobbin and the center core can be attained. Herein, in the former applications of Japanese patent application No. Hei 7-326800, Japanese patent application No. Hei 8-249733, the elasticity epoxy resin (the insulation resin between the secondary bobbin and the center core) is described that the elasticity epoxy resin is less than a room temperature, however the relationship with the secondary bobbin is not studied.
Further, relating to the above stated third invention, in the above stated secondary bobbin, it proposes that there is a thermoplastic resin having the coefficient of linear thermal expansion 10-45xc3x9710xe2x88x926 at the flowability direction and the cross direction during the molding at a range of the normal temperature (20xc2x0 C.)-150xc2x0 C. and this insulation resin is the soft epoxy resin having Young""s modulus of an elasticity less than 1xc3x97108 (Pa) at more than the glass transition point (a correspondence to claim 8).
A fourth invention (claim 4 correspondence) is characterized in that the insulation resin (the insulation soft resin) which satisfies the condition of the glass transition point Tg in the third invention is carried out the compression molding between the above stated secondary bobbin and the center core.
With the above stated methods, a volume of the voids which are contained in the resin is contracted to {fraction (1/200)}, and the voidless performance is carried out more, as stated in the above, in the insulation resin (for example, the soft epoxy resin) which is desired to the thin layer structure having one figure level mm at a decimal point, this voidless can devote largely to ensure the insulation performance.
Further, in the secondary bobbin the center core and the magnet are inserted inside toward an axial direction, the above stated soft epoxy resin covers these members and a fixing force at the axial direction of the center core and the magnet is increased by the compression molding and further an anti-vibration performance can be improved.
The compression molding of the insulation resin is carried as a following, for example. Namely after the above stated resin is vacuum potted, under the atmosphere the resin is the thermoplastic resin which is heated and hardened under the atmosphere. The above stated compression molding utilizes the difference pressure in which the vacuum changes to the atmosphere (a correspondence to claim 6).
A fifth invention (an invention relating to claim 5) is that, in the secondary wire being arranged inside primary wire structure individual ignition type ignition coil for use in an engine in which at an upper portion of a coil case a circuit case having a connector is installed inside an ignition unit of the ignition coil, an insulation resin is filled up between said secondary bobbin and said center core and at an upper end opening of said secondary bobbin said insulation resin is carried out a compression molding and a dent is formed at said upper end opening of said secondary bobbin, in said circuit case having said connector, a bottom portion of said circuit case is communicated to an upper portion of said coil case,a molding resin is filled up extending over between from an interior portion of said circuit case having said connector to said secondary coil and said primary bobbin of said coil case and between from said primary coil to said coil case, and said dent formed on said insulation resin is buried by said epoxy resin.
In the secondary wire being arranged inside primary wire structure type individual ignition type ignition coil, the merit (the voidless promotion) for filling up the insulation resin between the secondary bobbin and the center core (for example, the soft epoxy resin) according to the compression molding has stated already in the above.
In the secondary bobbin for accommodating the center core, in a case where the above stated insulation resin is filled up and is carried out the compression molding (for example, in a case where the resin is vacuum potted and the vacuum pressure and the atmosphere pressure after the atmosphere release) by separation other coil elements (the primary bobbin, the coil case, the circuit case on above the coil case, etc.), an earthenware mortar shape dent (a hemisphere shape dent) is left on the insulation resin face which positions an upper end opening face of the secondary bobbin. By the provision of this dent portion of the insulation resin, the concentrated pressing force is acted to the axial direction of the center core, the magnetic vibration etc. Generated in the center core which is constituted by the laminated steel sheets can be restrained effectively, as a result the anti-vibration performance can be improved more. In particularly, in the case where this insulation resin is the soft material, in comparison with the hard material resin the restriction force against to the center core is weakened, to compensate the above it is effective that the above stated dent portion is established to the upper end opening position of the above stated secondary bobbin.
However, in a case where the above stated dent is left, when the case of the ignition circuit is arranged on the coil case upper portion (the coil portion upper portion), since a gap is left between the center core and a metal base in the circuit case, a following inconvenience causes.
Namely, the surrounding portion of the center core is insulated, further the center core receives an affect of the electric field, as shown in FIG. 9, it is considered that the center core has an intermediate potential between the low voltage side and the high voltage side of the secondary coil. For example, in a case where the generation voltage of the secondary coil is about 30 kV, the center core has the intermediate potential of 15 kV. On the other hand, since the metal base which positions at an upper portion of the center core is grounded, when the gap exists between the center core and the metal base, the electric field concentration causes and further the insulation destroy causes.
According to the present invention, since the dent portion (the gap) caused by the compression molding of the insulation resin is buried by the epoxy resin (the epoxy resin which is filled up extending over from the circuit case to the secondary coil, the primary bobbin, and the primary coil, the coil case) which is filled up after the resin fill-up, the above stated electric field concentration can be mitigated widely and as a result the insulation performance between the center core and the metal base can be secured.
Further, the fill-up working of the epoxy resin for burying the above stated dent portion is carried out together with the potting and hardening working of the epoxy resin in which a bottom portion of the circuit case having a connector is communicated to the upper portion of the above stated coil case and extending over between from an interior portion of the circuit case having the connector to the secondary coil and the primary bobbin of the coil case and between the primary coil to the coil case, the rationalization of the working performance can be attained.
Further, in relating to the above stated fifth invention, following matters will propose.
Namely, a sixth invention (an invention relating to claim 9) is that, similarly to the above primary wire being arranged inside primary wire structure individual ignition type ignition coil for use in an engine in which said ignition coil is connected directly to a respective spark plug of said engine, an insulation resin is filled up between said secondary bobbin and said center core, at an upper end opening of said secondary bobbin said insulation resin is carried out a compression molding and a hemisphere dent is formed at said upper end opening of said secondary bobbin, in said circuit case having said connector, a bottom portion of said circuit case is communicated to an upper portion of said coil case, an epoxy resin is filled up extending over between from an interior portion of said circuit case having said connector to said secondary coil and said primary bobbin of said coil case and between said primary coil to said coil case, and said hemisphere shape dent formed on said insulation resin is buried by said molding resin.
With the above stated construction, in addition to the operations and the effects of the fifth invention can be expected, since the dent which is formed at the upper face of the insulation resin positioned at the upper end opening position of the secondary bobbin presents the hemisphere shape, since at the above stated gap (the dent) in which the insulation resin is buried a corner does not exist, even the molding resin is filled up in the dent, the voids are hardly left, as a result the good adhesion performance at the dent boundary face between the insulation resin and the molding resin which is potted in the above can be held.
A seventh invention (an invention relating to claim 12) proposes relating to the above stated ignition coil following engine having a plastic head cover.
Namely, an engine having a plastic head cover, characterized in that a cylinder head of the engine is covered by a plastic head cover; a respective spark plug mounted in said cylinder head is connected directly to an individual ignition type ignition coil which is prepared for each of said spark plug, said individual ignition type ignition coil comprises a coil portion in which a center core, a secondary coil wound on a secondary bobbin and a primary coil wound on a primary bobbin are installed concentrically inside a thin narrow cylindrical shape coil case, and a circuit case having a connector which is provided at an upper portion of said coil case and has an ignition circuit unit inside, said coil portion is penetrated through said plastic head cover and the center of gravity of said ignition coil is positioned at a lower position from said plastic head cover, and said circuit case having said connector is fixed to an outer face of said plastic head cover.
Further, the present invention is able to adopt to irrespective of the secondary wire being arranged inside primary wire structure type and the secondary wire being arranged outside primary wire structure type.
To accompany with the light weight structure of the engine, a need for a plastic structure of a head cover for covering a cylinder head of the engine heightens and to realize this the development has done. As to such a need, in a case where the individual ignition type ignition coil is mounted to a plastic head cover, it is necessary to improve following matters.
For example, in the individual ignition type ignition coil, the ignition coil being used actually is one as shown in FIG. 10. This ignition coil type has a coil portion 150 at an apex portion of a coil main body which comprises the coil portion 150 (a primary coil 153 and a secondary coil 155 are wound to a closed magnetic path core 159) and a rubber boot for combining a plug and this coil portion 150 is installed to a head cover 160 of the engine by means of a screw member 27.
To a plug hole 161 for mounting a spark plug 22, a conductive rod (Al rod) 156 for supplying a high voltage energy to the secondary coil 155, a coil spring member 158 connected to the conductive rod, and a rubber boot 157 for covering these components are mounted inside. And at a lower end of the rubber boot 157 the apex portion side of the spark plug 22 is fitted into and the spark plug 22 is connected to the high voltage side of the secondary coil 155 through the spring 158 and the conductive rod 156. Reference numeral 100 denotes a cylinder head of the engine, 151 denotes a coil case, 151a denotes a connector, 152 denotes a primary bobbin and 154 denotes a secondary bobbin.
In a case where the above stated type individual ignition type ignition coil is installed to the plastic engine head cover, since the coil portion is positioned above the head cover and further the center of gravity is positioned above the head cover (the center of gravity is high), the coil portion vibrates together with the engine vibration and acts the swing operation. So that so as far the plastic head cover is formed strongly and increases the rigidity, the head cover itself is not protected and the vibration of the coil portion is not restrained, as a result it is impossible to attain the light weight structure of the head cover (the light weight structure of the engine).
The inventors of the present invention have found out following necessities in which according to the above stated facts a burden of the plastic head cover can make small and to mount the individual ignition coil the center of the gravity of the ignition type ignition coil and further the swing operation is formed small by supporting at least two points of the axial direction of the ignition coil main body.
Under the above stated knowledge, the present invention is constituted, according to the construction, the head cover of the engine is made of the plastic material, in a case where this head cover is installed to the individual ignition type ignition coil, the center of the gravity of the ignition coil is positioned at a low position of the engine head cover, and further the comparative light weight circuit case having the connector in the pencil type coil is fixed (for example, the screw fixing) to the outer face of the plastic head cover, and at this fixing portion and the plug hole combination position of the plug hole two point support mechanism of the axial direction can be obtained. As a result, the vibration of a whole ignition coil is made small and further the vibration of the ignition coil which is given to the plastic head cover can be restrained, the light weight structure (the thin thickness structure) and simplification of the plastic head cover can be attained, and further the mount of the individual ignition type ignition coil can be realized.